1. Field of the Invention
The present invention relates to a method and device for checking the tightness of structural seals. The invention relates in particular to a method for detecting damaged or faulty points, in particular weak points having a reduced material thickness in a membrane-type, electrically non-conductive or only poorly conductive structural seal which has a high electrical disruptive strength by comparison with air and is provided with an electrically conductive layer which is arranged inside or outside the structural seal and extends over substantially the entire surface of the structural seal and to which an electrical test voltage is applied, and to a membrane-type structural seal, which is made of electrically non-conductive or only poorly conductive material and has a high electrical disruptive strength by comparison with air, comprising a test device having an electrical voltage source for detecting damaged or faulty points, in particular weak points having a reduced material thickness in the structural seal, and comprising an electrically conductive layer which is arranged inside or outside the structural seal and extends over substantially the entire surface of the structural seal.
2. Description of Related Art
Thus far, membrane-type seals have represented a considerable proportion of structural seals. The purpose of structural seals is to protect the building reliably against the penetration of groundwater, earth moisture and rain water and thus to prevent damage to the basic structure and limitations on the use of the building over the entire life of the building. Membrane-type seals generally consist of bituminous masses or of the mass plastics materials which are available nowadays, and industrially are produced generally as web-type products but also increasingly as sealing masses to be applied to surfaces on the building site. To carry out their function, membrane-type seals have to be water-tight.
Product defects, faulty processing, inappropriate loads and the effect of weathering can lead to a loss of tightness in membrane-type structural seals, and this can cause extensive further damage to the building if the damage is not identified soon enough in order to be eliminated immediately in a targeted manner. Thus, the majority of damage to buildings thus far has been caused by damage to the structural seals. Further, systematic damage elimination is often impossible even if the seal is known to be damaged, since the damaged point cannot be located and is often inaccessibly embedded in the structure of the building. Damage to membrane-type structural seals thus involves considerable damage potential.
Against this background, there have already been attempts for many years to provide options for monitoring tightness and locating leaks in structural seals, with the aim of recognising damage to seals as soon as possible and locating this damage as precisely as possible. The presently available solutions are characterised by the following properties:
Systems of a simple, conventional type: in these systems, the seal is constructed in such a way that on the side of the seal intended to be dry, a visual checking option is provided in such a way that penetrating leaked water can be identified in the course of an inspection. By adding electrical moisture detectors, the monitoring can also be automated. A disadvantage of this construction is that it is virtually impossible to locate leaks, and leaked water also cannot be distinguished from the appearance of condensation water, in such a way that decisive leak identification is not possible in practice. A further disadvantage is that a check on the seal is always dependent on the seal being loaded or already having been loaded with water at the time of the test.
Vacuum systems: in these systems, the seal is constructed with two layers in such a way that there is an exhaustible intermediate space between the seal layers. If the control space is evacuated to a particular negative pressure, the tightness of the seal can be determined based on the increase in pressure over time. An advantage of this system is that the tightness of the seal can also be determined independently of water-loading. Disadvantages of the method are the high costs of the double seal system and the lack of an option for locating the damaged point in a targeted manner in the case of a leak.
Electro-resistive systems: these systems exploit the fact that, in terms of the material thereof, membrane-type seals have a high electrical resistivity and a high disruptive strength. Various configurations are available:
In potentiometric methods, the electric potential field which arises when an electrical voltage is applied between the wet seal exterior or the contact layer, or the building structure if there is no contact layer, is determined on the wet exterior of the seal or in an electrical contact layer on the side intended to be dry underneath the seal by passing an electric current through the leak point. These methods can be very effective, depending on the technical implementation, and in some cases make fully automatic tightness monitoring and precise location of leak points possible.
Patent DE 41 25 430 C2 discloses a sealing film having an internal conductive layer which is covered with an electrically non-conductive layer on each of the two sides. If there is a leak in this seal, the occurrence of the leak can be identified by measuring the current flowing from the conductive layer towards the earth or towards the conductive support medium.
A disadvantage of these methods is that leak identification is basically only possible when the seal is loaded with water or wet covering material and a conductive path has formed at the leak point by way of penetrating moisture. If the measurement is carried out from the upper seal surface, the entire seal surface must be examined manually with the test device in order to check the seal. This requires a considerable amount of time and only produces reliable results with sufficient specialist knowledge.
This disadvantage is overcome in high-voltage test methods by using a movable test electrode, known as a spark brush, to apply to the uncovered side of the seal, facing away from the building, a high voltage, the counter pole of which is either the earthed building structure on which the seal is laid or an additional conductive layer on the side facing the building immediately below or behind the seal, the layer either lying loosely below or behind the seal or being firmly connected to the seal as disclosed in patent application WO 00/01895 A1. If the test electrode is then guided over a damaged point in the seal, the disruptive strength there is reduced by comparison with the intact seal surface, either because the material thickness is lower than in an intact seal as a result of the damage or because there is merely an air gap which has a considerably lower disruptive strength than the seal material. As a result of these conditions, a spark is ignited upon passing over a damaged point. This is detected by the device and a leak is thus reliably identified. So as to be able to work only with relatively low test voltages, in some available systems the test is carried out with a water spraying device instead of a spark brush, in such a way that the voltage is applied to the seal via the water jet, which then also penetrates into capillary-type damaged points and thus produces a conductive connection at the damaged point.
A disadvantage of known high-voltage test methods is that the seal must be completely uncovered, and if these methods are applied using water as a test medium, water can run off and produce an electrical connection via the edge of the seal, distorting the measurement result. Since the entire seal has to be examined with the test electrode for testing, the method is very time-consuming, in particular when large or poorly accessible seals are to be tested. If not the entire surface is brushed with the test electrode during testing, which cannot be systematically monitored, there is a risk of incorrect measurements. The known high-voltage tests are thus not suitable for testing building seals systematically during subsequent building work, since in this case it is often no longer possible to access the seal.
In particular in tunnel seals, seal damage is a very significant risk, since seal damage is generally first identified when water enters the finished tunnel, since the drainage must initially be ceased before the hydrostatic loading pressure on the seal is set and the seal is first loaded with water. The pressure build-up in this case results in a further risk of damage to the seal, since as the external pressure increases, the seal is pressed more and more strongly against the concrete inner shell. If regions of the inner shell are not completely filled with concrete, the seal is pressed against the uncovered reinforcement of the inner shell and perforated, in such a way that there are further risks of damage. The problem is aggravated by the fact that the water, as has been found by experience, does not exit the concrete inner shell in the place where the leak in the seal is actually located, but finds a path behind the concrete inner shell until it exits at leaky gaps in the joints between tunnel segments or through cracks in the concrete in the tunnel tubes.
Since the seal is concealed behind the tunnel inner shell in such a way that it cannot be inspected, and no information or only vague information as to the position of the leak is available, repairing leaks in tunnel seals has thus far required expensive injection processes over a large area, which in spite of the great expense are often unsuccessful, in such a way that a large number of tunnels remain leaky despite repairs and permanently generate considerably increased maintenance costs. Thus, in its annual report for 2004, the Swiss Federal Laboratories for Materials Testing and Research (EMPA) reported on the results of a joint research project with the Swiss Federal Roads Office (FEDRO), in which a total of 63 Swiss tunnels were tested for the effectiveness of the sealing systems thereof. Subsequently, even after repairs to the established leaks by injection processes, 13 tunnels were still classified as leaky, of which only 10 were tunnels containing compressed water. Against the background of these disappointing results and in view of the immense costs of the (often unsuccessful) repairs and maintenance of leaky tunnels, the report concluded with the urgent appeal to do everything possible to make tunnel seals tight from the start.
However, this aim can only be achieved if the quality of the seal, and thus in particular the tightness thereof, can be tested during construction and soon after the individual phases of constructing the building, damage can be established systematically via stable, objective measuring results, established damage can be located in a simple manner, and defects or weak points in the rest of the building work which can be lead to damage to the structural seal, such as incomplete concreting, are likewise systematically detected and eliminated by suitable processes before damage to the seal occurs as further damage.